Conventional parboiled rice is a kind of processed rice that is produced and eaten mainly in the Asian region including India and Pakistan and in some parts of America and Europe.
The parboiled rice has been manufactured by steaming unhulled rice after sufficient soaking to gelatinize starch of rice grains and then performing drying, hulling, and milling. For this reason, endosperm is impregnated with, e.g., the smell of a hull and has a flavor of hull.
Parboiled rice free of hull smell has been developed in recent years to meet diversified tastes of consumers, and manufacturing methods for the parboiled rice have been proposed (see Patent Literatures 1 to 3).
The manufacturing methods described in Patent Literatures 1 and 2 include a process of subjecting brown rice as a raw material to partial milling treatment, subjecting grains of the rice subjected to the partial milling treatment to water addition treatment with, e.g., a mist or moist forced air, subjecting the moisture of the rice grains subjected to the water addition treatment to tempering treatment, subjecting the rice grains with the moisture subjected to the tempering treatment to atmospheric steam-boiling treatment with steam, subjecting the rice grains subjected to the atmospheric steam-boiling treatment to pressurized steam-boiling treatment with pressurized steam, subjecting at least the surface of each rice grain subjected to the pressurized steaming to cooling treatment, subjecting the rice grains subjected to the cooling treatment to finish milling treatment, and subjecting the rice grains subjected to the finish milling treatment to drying treatment.
Since the manufacturing methods include steaming of brown rice, parboiled rice free of hull smell can be obtained.
At the manufacture of parboiled rice, rice grains need to be subjected to water absorption as pretreatment of pressurized steam-boiling treatment in order to gelatinize starch of each rice grain to the center through the pressurized steam-boiling treatment. In contrast, the manufacturing methods subject rice grains to water absorption not through soaking treatment but through water addition treatment and do not need use of a large amount of water and provision of drainage treatment equipment.
In the above-described manufacturing methods, however, if the amount of water added is increased to accelerate the speed of water absorption of rice grains at the time of the water addition treatment, a crack may appear in the surface of each rice grain to degrade the appearance quality of the rice grain.
Additionally, the parboiled rice manufacturing apparatuses described in Patent Literatures 1 and 2 each include a piece of dedicated equipment for each treatment in the above-described manufacturing method and suffer from the problem of increasing the overall size of the apparatuses.
The manufacturing method described in Patent Literature 3 subjects brown rice to preliminary pressurized steam-boiling treatment, prior to the above-described water addition treatment in the manufacture of parboiled rice described in Patent Literatures 1 and 2 described above.
According to the manufacturing method, starch of each rice grain is gelatinized only at a surficial portion by the preliminary pressurized steam-boiling treatment, and the surface of the rice grain is toughened by a gelatinized layer. For this reason, even if the amount of water added is increased to accelerate the speed of water absorption of rice grains, a crack does not appear in the surface of the rice grain. The manufacturing method allows manufacture of parboiled rice, grains of which have good appearance quality.
The parboiled rice manufacturing apparatus described in Patent Literature 3, however, also includes a piece of dedicated equipment for each treatment in the above-described manufacturing method and suffers from the problem of increase in overall size.
There is also proposed an apparatus for manufacturing parboiled rice in batches (see Non Patent Literature 1).
The manufacturing apparatus described in Non Patent Literature 1 subjects unhulled rice or brown rice to pressurized steam-boiling treatment inside a container and dries the brown rice or the like subjected to the pressurized steam-boiling treatment inside the container. A plurality of treatments can be performed inside the same container.
The manufacturing apparatus described in Non Patent Literature 1 described above, however, includes two large tanks for subjecting the brown rice or the like to soaking treatment as pretreatment of the pressurized steam-boiling treatment.
For this reason, the manufacturing apparatus described in Non Patent Literature 1 described above requires provision of large drainage treatment equipment and does not necessarily solve the problem of increase in overall size.